Coaxial switch



y 8, 1957 JO EMMETT JENNINGS ETAL 2,794,087

COAXIAL SWITCH Filed June 10, 1955 //V VE N 7 UPS L/O EMMETT dE/V/V/NGS TED N 77LM/4/V MA 694/ their A7 TOR/VEY United States PatentO COAXIAL SWITCH Jo Emmett Jennings and Ted N. Tilman, San Jose, Calif.,

assignors to Jennings Radio Manufacturing Corporation, San Jose, Calif., a corporation of Caiifornia Application June 1%, 1955, Serial No. 514,496

14 Claims. (*Jl. flitt ill} Our invention relates to coaxial switches; and particularly to a coaxial switch of the vacuum type.

One of the objects of our invention is the provision of a coaxial switch of the vacuum type which is capable of being controlled from a remote point.

Another object of our invention is the provision of a coaxial switch capable of broad band operation in both V. H. F. and U. H. F.

Still another object is the provision of a coaxial switch in which the disconnected mobile contact means is automatically grounded to prevent capacitance between the high potential contact and the disconnected mobile contact means.

A further object is the provision of a coaxial switch in which transmission impedance is substantially a constant throughout the switch.

Other objects of the invention include the provision of a switch in which the actuating mechanism has no tendency to disturb the low standing-wave ratio of the switch, the contact resistance is low due to the use of copper contacts, and there is no oxidation of the contacts to cause deterioration thereof.

Other objects will be brought out in the following description of the invention. We do not limit ourselves to the showing made by said description and drawings, since we may use variant forms of the invention within the scope of the appended claims.

Referring to the drawings:

The figure is a horizontal sectional view of our switch. A portion is broken away to reduce the length of the figure. The structure omitted on the right of the figure is a duplicate of that shown on the left.

Broadly considered, the vacuum coaxial switch of our invention comprises a hermetically sealed and evacuated metallic housing at ground potential, within which are enclosed a plurality of high potential conductors and contacts. Preferably, at least one of the contacts is fixed with relation to the housing, and may be designated as the high potential stationary contact through which the switch is energized from a high-frequency power source. Each of the other contacts is arranged to selectively connect or disconnect an associated hollow conductor with the energized stationary contact, either singly or in combination, so as to redirect the high potential energy through the selected hollow conductor or conductors to the associated coaxial transmission line or lines.

The metallic housing is maintained at ground potential, and means are provided for insulating the stationary contact and conductor from the housing, and for automatically grounding the mobile contact means and its associated hollow conductor when they are disconnected from the stationary contact.

Means responsive to remote control are provided to effect selective operation of the mobile contact means to close or open a circuit or circuits through the switch. Leads electrically insulated from the housing, electrically and mechanically connect the conductors to associated transmission lines.

2,794,087 Patented May 28, 1957 In television broadcasting, the need for remote control switches for fast shifting of circuits in coaxial transmission lines is very great. The switch necessary for a particular installation may be of the multiple pole, multiple throw type, or it may take the form of a single polesingle throw, or single pole-double throw type switch. Whatever form the coaxial switch takes, basic advantages are provided by arranging the contact elements in a vacuum. If this vacuum coaxial switch is designed for control from a point remote to its installation, additional advantages flow from its use. A proper installation of our coaxial remote control switch eliminates the need for manual rearrangement of circuits and provides for instant remedial correction in case of equipment failure and other emergencies.

Specifically, our switch is applicable in radio-frequency power circuits extending between the transmitter and antenna, where it permits convenient, remote control of such functions as power cutback, dummy load switching, transmitter and antenna switching, and other functions familiar to those skilled in the art.

The switch is preferably enclosed in a hermetically sealed, T-shaped metallic housing of such size and proportions that it may be conveniently interposed in the transmission lines with which it is to be used.

The housing is conveniently formed by a pair of open ended tubular sleeves 2, projecting in opposite directions from a centrally positioned junction block 3; and together form the main portion of our switch. A third sleeve 4, projecting from the junction block at substantially a right angle to the sleeves 2, forms a transverse portion. The sleeves and body are formed from copper, the parts being brazed together to form an integral and rigid T-shaped housing which may be hermetically sealed and evacuated to provide a vacuumized chamber 5, extending on each side of the junction block 3.

Hermetic sealing of the housing is conveniently accomplished by interposing a low electrical loss dielectric annular wall 6 in each of the sleeves 2 and 4 at a point spaced from its open end. Each dielectric annulus is axially aligned within its associated sleeve, and held rigid by a cylindrical copper apron or bushing 7. One end 8 of the bushing encloses and is integrally brazed to the metallized outer periphery of the dielectric annulus, while the other end 9 of the bushing fits tightly Within the inner peripheral surface of the associated sleeve. Brazing this: end of the bushing to the housing effectively supports the annular dielectric wall 6 in a mechanically rigid and axially aligned position.

The metallized inner periphery of each dielectric wall encloses and is brazed to one end 12 of a cylindrical copper mounting apron or sleeve 13 adapted to receive and rigidly secure in position, the high-potential energy carrying elements of the switch. These include a stationary contact 16 centrally located within the junction block 3 at the intersection of axis lines 17 and 18, corresponding to the main and transverse portions of the housing respectively.

The stationary contact 16 is preferably formed by a short length of copper tubing axially aligned in relation to axis line 17, and cutoif squarely at each end to provide annular contact surfaces 21 and Z2. perpendicular to the axis 17. We have found that a convenient length for the contact is one equal to its outside diameter, which corresponds closely to the diameter of the transmission line inner conductor with which the switch will be used, 'so that constant impedance results.

To hold the stationary contact mechanically. rigid, and to form a conductive path thereto, we braze the. stationary contact on the inner end 23 of a fixed tubular copper conductor '24 axially aligned on the axisline 18 of sleeve 4. At a point spaced outwardly from its inner end, the conductor is provided with an exterior annular shoulder 26 against which the axially projecting end of the mounting apron or sleeve 13 abuts. The proportions of the parts are such that thesleeve ,end fits closely around the conductor adjacent the shoulder, Where it is brazed to provide an integral and rigid mounting. The reduced portion 27 of the conductor extends outwardly through the mounting sleeved?) and annular dielectric wallf6, and terminates flush with the end of sleeve 4. t a

Brazed within the outer .end of the reduced portion 27 of tubular conductor 24 is a copper plug 28. The plug extends beyond the conductor in a reduced portion 29 serving as a mount for the low electrical loss insulator 31. A standard coupling fitting 32, secured by cap screw 33 to the .plug, retains. the insulator in abutting relationship against the end of sleeve 4. A copper sleeve 34 surrounding reduced portion 27 of conductor 24, extends between insulatorso and 31 and acts to lend additional rigidity to the assembly. If desired, the sleeve 34 may be brazed to the conductor 24. A straight coupling sleeve 36, surrounding the extreme end of sleeve 4, serves to connect the switch into a transmission line circuit, preferably a source of high potential radio-frequency power.

It will be noted that stationary contact 16 is rigidly mounted in a position coaxial with the main portion and insulated from the surrounding housing by electrical grade aluminumoxide ceramic insulators 6, 31 and 76 such as Coors AI-ZOO.

Mounted within the main housing portion, within each of the sleeves 2 and coaxially aligned therewith, is a mobile contact means, positioned so as to be engageable with the stationary contact 16. The mobile contact means is conveniently spool shaped, having belled ends 37 and 38 connected by a reduced neck portion 39. The belied end 37 is provided with an annular contact flange 41 proportioned to engage with stationary contact surface 21. Copper is preferable for the contacts because of its low resistance at radio frequencies.

The contact is movably supported coaxially of the main housing portion by a collapsible bellows and bearing assembly including bellows 42, slide bearing 43, and piston rod 44 carried by the slide bearing. The inner open end of the bellows is provided with a copper plug 46 brazed therein, through which the threaded outer end 47 of piston rod 44 projects. The belled end 38 of the contact is threaded onto the end of the rod until it jams against the plug, when all of the parts are integrally brazed to form a continuous, mechanically strong and rigid construction. In the embodiment shown, theswitch is designed to have contacts normally closed, but it will be understood that the switch could be as easily designed to provide normally open contacts.

The outer end of the bellows abuts against the annular shoulder 48 formed .on the outer periphery of slide bearing 43 intermediate its ends, where it is inte rally united to provide an air-tight and mechanically rigid and continuous conductor with the slide bearing. eyond the shoulder, the slide bearing extends through and is brazed to mounting apron or sleeve 13, here again providing a mechanically rigid and hermetic seal. The portion 49 of the bearing which projects through the sleeve is co-unterbored and provided with vents St) to provide communication between the bellows interior and the atmosphere. At its outer end the hollow conductive portion 49 is provided wtih a reduced threaded portion 51 on which is threaded the mobile contact actuating mechanism.

The actuating mechanism for each of the mobile contacts includes cylinder 52 having a bore 53 within which a piston may reciprocate. The piston is fixed on the of piston rod 44, and moves in bore 53 in response to the application and release of air pressure in the chamber 55 connected through dielectric conduit 56 to the atmosphere and to a source of air under pressure by the three-position valve 57. The valve 57 may be operated manually or by conventional remote control means, as desired. Bearing rings 5%, abutting the portion 51, slidably support the rod adjacent its piston end, and with O-ring gaskets 59, form the forward wall of the air chamber 55. The valve 57 serves to selectively control pressure in the chamber 55 to overcome atmospheric pressure to move the piston to disconnect the mobile contact from the high potential stationary contact, or to permit atmospheric pressure to expand the bellows and efiect engagement of the contacts. Bleed passage 61 provides for the escape of air from the bore 53 when the piston is moved back by pressure in chamber 55.

It will be noted that bellows 42, slide bearing 43 and air cylinder 52 form a continuous conducting path for radio frequency energy between the movable contact and coupling fitting 63, fixedly secured on the outer end of the air cylinder by the cap screw 64. An insulator 66, interposed between the air cylinder and the coupling sleeve 36, insulates the conducting elements from the grounded housing. The insulator es, cooperating with insulator 6 and mounting sleeve 13, hold the assembly in a mechanically rigid coaxial position free from vibration.

in order to eliminate capacitance between the contacts 41 and 21 when they are disconnected and held in spaced relation, means are provided for automatically grounding the disconnected mobile contact. Brazed within the main housing portion at the juncture of each sleeve 2 with the block 3, is a copper grounding ring 71. The grounding ring is provided with a bore 72 normally encircling the neck portion 39 of the mobile contact when the contact is conducting. In this position of the parts, the diameters of the bore and neck bear a relationship which will insure constant impedance transmission through the switch. The bellows. preferably beryllium-copper, is selected for proper impedance match, since it forms a part of the conducting path.

When the movable contact is disengaged by admission of pressure air to chamber 55, the contact moves away from stationary contact 1-6, coming to rest when flange 41 on the contact engages in counterbore '73 formed in the grounding ring. In this position of the parts, the mobile contact is mechanically supported and grounded; and there can be no transfer of energy due to capacitance between the high potential stationary contact and the disconnected movable contact. Release of the pressure air from chamber 55 permits atmospheric pressure to expand the bellows and reengage the contacts. Since engagement is accompanied by the application of considerable force on the stationary contact, means are provided to insure the lateral stability thereof. This is accomplished by passing one end of a snug fitting ceramic pin or post 76 through aligned apertures77 in the contact and into the bore 78 in the endof conductor 24. This end of the ceramic post fits snugly in the bore 78 but permits axial movement of the post to compensate for variations in the expansion and contraction of adjacent parts. At its other end the ceramic post is metallized and provided with a copper cap 7? soldered thereon. A plate 81, having a central aperture 82 and a peripheral flange 83, is interposed between the soldered cap 79 and the wall of junction block 3. Solder applied in the aperture 82 rigidly secures the plate to the cap; Brazing or soldering the flange 33 to the wall of junction block 3 provides a hermetic and mechanically rigid support for the ceramic post, capable of absorbing a considerable amount of lateral force.

Thus it will be seen that by selective operation of the valves 57, by remote control or otherwise, the movable contacts of the switch may be moved to close or open the circuits therethrough. Since the air in the dielectric conduit 56 is a good insulator, there is no tendency for radio-frequency energy to flash over at this location; and

there is no tendency to disturb the standing-wave ratio of the switch.

We claim:

1. A coaxial switch for coaxial transmission line circuits comprising a metallic housing having a main portion and a transverse portion, a dielectric wall across each portion of the housing and enclosing therewith a vacuumized chamber, a hollow conductor coaxial with the main housing portion and extending through its wall and hermetically sealed thereto, a second conductor coaxial with the transverse housing portion and extending through its wall and hermetically sealed thereto, a slide bearing coaxially disposed on the hollow conductor, a bellows having a mobile end within the chamber and continuous with the hollow conductor to close hermetically the inner end thereof, mobile contact means within the chamber continuous with said mobile end, means within the hollow conductor and including a piston and piston rod fixed to said mobile end for controlling said mobile contact means, and stationary contact means fixed on the second conductor and engageable by the mobile contact means.

2. The combination of claim 1 including lead means for coupling the conductors into a circuit.

3. The combination of claim 1 including means to electrically ground the mobile contact means when it is out of engagement with the stationary contact means.

4. The combination of claim 1 including dielectric means spaced from each said dielectric wall and interposed between each conductor and its respective housing portion to mechanically support the outer end of each conductor.

5. The combination of claim 1 in which the bellows and hollow conductor are proportioned to provide constant impedance transmission therealong.

6. The combination of claim 1 including means to electrically ground the mobile contact means when it is out of engagement with the stationary contact means, said grounding means and mobile contact means having opposed surfaces proportioned to provide constant impedance transmission of radio-frequency energy when said mobile contact means is engaged with said stationary contact means.

7. The combination of claim 3 including means for mechanically supporting the mobile contact means in its disenagegd position.

8. A coaxial switch for coaxial transmission line circuits comprising a metallic housing having a main portion and a transverse portion, a dielectric wall across each portion of the housing and enclosing therewith a vacuumized chamber, a pair of opposed hollow conductors coaxial with the main housing portion, each hollow conductor extending through one of said dielectric walls and hermetically sealed thereto, a third conductor coaxial with the transverse housing portion and extending through its wall and hermetically sealed thereto, a slide bearing coaxially disposed on each hollow conductor, a pair of bellows having mobile ends within the chamber, each continuous respectively with a hollow conductor to close hermetically the inner end thereof, mobile contact means within the chamber continuous with each said mobile end, means within each hollow conductor and including a piston and piston rod fixed to each said mobile end for separately controlling each said mobile contact means, stationary contact means fixed on the third conductor and engageable by each said mobile contact means, and lead means for coupling each conductor into a circuit.

9. A coaxial switch for coaxial transmission line circuits comprising a metallic housing having a main portion and a transverse portion, a dielectric wall across each portion of the housing and enclosing therewith a vacuumized chamber, a hollow conductor coaxial with the main housing portion and extending through its wall and hermetically sealed thereto, a second conductor coaxial with the transverse housing portion and extending through its wall and hermetically sealed thereto, a slide bearing coaxially disposed on the hollow conductor, a bellows having a mobile end within the chamber and continuous with the hollow conductor to close hermetically the inner end thereof, mobile contact means within the chamber continuous with said mobile end, a wall within the hollow conductor and forming a piston chamber, a piston in the chamber, a piston rod connected at one end to the piston and at the other end fixed to the mobile end of said bellows for controlling said mobile contact means, and stationary contact means fixed on the second conductor and engageable by the mobile contact means.

10. The combination of claim 9 including dielectric conduit means connecting said piston chamber with a source of fluid under pressure, and valve means in the conduit to selectively control the pressure of fluid in said chamber.

11. A coaxial switch for coaxial transmission line circuits comprising a vacuumized metallic housing, a hollow conductor coaxial with the housing, and a dielectric annulus interposed between the housing and conductor and hermetically sealed to both and supporting the hollow conductor within the housing.

12. A coaxial switch for coaxial transmission line circuits comprising a vacuumized metallic housing, a hollow conductor coaxial with the housing, a dielectric annulus interposed between the housing and conductor and hermetically sealed to both and adjacent one end of the conductor, a stationary contact within the housing supporting the other end of the conductor when a circuit is closed thercbetween, and a metallic annulus engageable by said other end when the circuit is open, said metallic annulus electrically grounding and mechanically supporting said other end of the hollow conductor.

13. A coaxial switch for coaxial transmission line circuits comprising a vacuumized metallic housing, a hollow conductor coaxial with the housing, and a dielectric annulus interposed between the conductor and housing, and metallic aprons hermetically sealing the annulus to the housing and to the conductor.

14. A coaxial switch for coaxial transmission line circuits comprising a vacuumized metallic housing normally at ground potential, a stationary contact within the housing normally at high radio-frequency potential, a movable contact within the housing responsive to atmospheric pressure for normally engaging said stationary contact, means hermetically sealing the housing and normally insulating both contacts therefrom, means insulated from the housing for controlling said movable contact, and a terminal lead insulated from the housing for connecting each said contact into a circuit.

References Cited in the file of this patent UNITED STATES PATENTS 1,892,538 Prince Dec. 27, 1932 1,996,304 Millikan et al Apr. 2, 1935 2,509,217 Davis May 30, 1950 2,642,495 Haulman et al. June 16, 1953 FOREIGN PATENTS 355,535 Great Britain Aug. 27, 1931 

